Lower unit oil turning black on evinrude

[countryboy9799]

Hi all,

I have a 1982 70HP evinrude and for the last two times I have changed it the lower unit oil had been black, didnt look like there was any water in it. I dont remember it turning black when I have changed it before and was wondering what your thoughts where. Thanks

[theoilman]

Short of having an oil analysis done you will never get a completely accurate answer. You're right, normally black will not be water. Usually water, even as little as a few percent water, will turn frothy/milky. Have you changed brands of oil? Have you changed the specification of the oil you use? I have seen some automotive gear lubes that do not carry the marine specs turn black when used in an outboard lower unit, and I have no idea why. (I have not bothered with the expense of oil analysis to find out. Oil analysis will cost typically around $25.) I have never seen a marine spec. gear lube turn black.

[shamrock7]

Does the Lower unit grease smell burnt? If so, you probably have a bearing or gear issue that is causing excessive heat which is breaking down your grease.

[Surface Tension]

Gear oil has a pungent smell to begin with so the smell test can be deceiving. To turn black isn't normal. My first thought is heat. That could build up in two places. The lower unit, which could be the case but being in the water with good contact to the housing, seems unlikely. Another guess and might be more likely is the drive shaft bearing just below the water pump. This is in a spot of the drive that is under water but not in direct contact with water.

If you were low on oil or your bearing was wore it can create heat. If either were the case your looking at complete failure soon. Next thing to suspect is a bad impeller. Might be enough to cool the engine just enough to the point where it won't seize from over heating but to the point where the exhaust is very hot. That water that should be exiting out your through hub exhaust isn't there and your lower drive will get very hot. High heat exhaust with no water is coming out that through hub exhaust and could very well be scorching your gear oil.

About using Automotive Gear Oil instead of Marine Lower unit Gear Oil. The RPMs on a lower unit are extremely high, much higher then an automobile. The formulation between the two are different. Automotive gear oil in that high RPM situation will be whipped into a froth. It will have no choice but to expand. What happens next is your water tight sealed system gets blown from the pressure build up. There goes your seals. Gear oils leaks out and water moves in.

[countryboy9799]

I have been using pennzoil gear lube that is marine grade, bought at walmart if that helps. I do have a good stream of water coming out the hole on top if that helps also, I could change the impeller as its been awhile. The last time I changed the impeller was a few years ago and that was when my problem started.

The motor was ran for about 30 seconds out of water and ruined the impeller. How would that be connected to the problem I am having now? I know the prop turns easily so I doubt the bearings in the lower unit are bad but maybe as SF said it could possibily be the upper shaft bearing. I have been going two years on the oil change and I wonder if a bearing would hang in there that long, I wouldnt think so.

I have felt the lower unit temp by hand after it has been ran awhile and it has always been similar to the water temp, definatly not much warmer anyways. I would like to get this fixed before anything major breaks thats for sure. Is there any way that the exhaust can get into the oil where it may be getting sooty?

Thanks for the help guys.

[Surface Tension]

If exhaust was getting in then water would be getting in too.

The lower unit is made from aluminum. It could be that aluminum is going though oxidization and turning the gear oil black. 2 years on an oil change, this could start to show up I guess.

If the lower unit gear oil level has been been full, doesn't smell burnt, and you can't see any metal specs in the drain oil, you haven't been overheating, then you might just want to replace the oil and check it often.

As you found out running the outboard without cooling will ruin the impeller fast. Doesn't take long so I wouldn't do it even for a few seconds. Could something in the lower unit been damaged during that short run. If it did the hot exhaust going though the and around the lower unit would be the culprit.

[countryboy9799]

What does this mean if the aluminum is oxidizating? Maybe when I ran it without water it cooked the oil and it just needs to be cleaned up with some oil changes?

As far as metal filings I only found a few flakes of metal on the magnet which is normal. I will change the impeller before spring and do a mid season change next year, thanks for your help.

Scott

[Surface Tension]

Even run you hand along bare aluminum and it turned black?

[countryboy9799]

I haven't done this, really havent worked with aluminum much. What would this mean to me? Any future problems?